Technology update

Dec 4, 2017

Graphene composite provides wireless power at your fingertips

Recently developed triboelectric nanogenerators (TENGs) not only harness waste mechanical energy from the environment, but can wirelessly transmit energy and signals too. By building on fundamental crystal symmetry principles, researchers at Clemson University in the US have designed a graphene nanocomposite and incorporated it into TENGs that provides voltages great enough to wirelessly transmit the harvested energy to remote devices. The wireless TENGs realise a technology dream first envisioned by Nikola Tesla more than a hundred years ago and provide a potentially powerful contribution to the future Internet of Things.

Nikola Tesla’s "Most marvellous method to transmit power universally" made headlines back in 1897, and led to the initial construction of The Famous Tesla Tower in Long Island, New York – a 187 foot behemoth topped by a giant sphere 68 feet in diameter that was never finally completed. One hundred and twenty years later, the research team at the Clemson Nanomaterials Institute has now realised a new wireless power transmission device, beyond Tesla’s model, from a 3D printed nanocomposite of graphene and polylactic acid. The device – the first renewable energy generator capable of wireless transmission – can generate electric fields of 2400 V from a tap of the fingers, and can transmit binary code over 3 metres.

The power of symmetry

In line with the eco-friendly sustainability motivations of developing renewable energy sources, the Clemson researchers were keen to identify a material that was earth-abundant, biodegradable and recyclable. The tribo- or piezoelectric properties of a material are determined by the crystallographic symmetry of the material, and vanish when the crystal lattice has a centre of symmetry. However, the Clemson research team built on previous work by researchers in Japan showing they could remove the centre of symmetry of a biopolymer by adding polarizing molecules to asymmetric carbon atoms in its chemical structure.

Polylactic acid has many of the material attributes the researchers were looking for – it is plant- derived and biodegradable, and contains two asymmetric carbon atoms. However, its electrical resistance is too high for TENG devices, so the researchers used graphene as a filler to produce a nanocomposite that they could combine with the highly electronegative polymer Teflon in 3D-printed wireless TENGs.

"We were not surprised by the high voltage generation, but we were awed at the ability to transmit and receive wireless signals without any interference from the surrounding environment, such as WiFi, mobile phones, power outlets, etc," explain Podila and his colleagues. They demonstrated the energy harvesting and transmission capabilities of their device on a range of domestic appliances including smart-tint windows, photoframes, LED displays and a call bell/security alarm.

The future of W-TENG

3D printing allows inexpensive scalable fabrication of wireless-TENG (W-TENG) devices, with different patterns to increase the efficiency, and with several W-TENG layers in series. It also opens up future opportunities to integrate device fabrication with the automotive, textile, and electronics industry.

An exciting application for the device is a smart walkway that could harness mechanical energy from the footfall of passers-by. Energy-scavenging walkways may sound like science fiction, but the researchers are already patenting the technology and envision working closely with industrial partners to bring it to the market in the next two to three years.

Other potential uses of the W-TENGs include low-power lasers, photodetectors and biosensors free from power-outlet requirements. The researchers describe this "cutting the cord" approach as "need-of-the-hour for improving healthcare in low- and middle-income countries with no reliable electrical power".

The researchers are now developing two-dimensional sheet-like materials "beyond graphene" as more environmentally friendly alternatives to Teflon that also boast higher electrical conductivities. Future work also includes the development of "fingerprint"-sensitive user-specific W-TENGs for home-security applications. Co-authors Sai Sunil Kumar Mallineni and Herbert Behlow are focusing on the development of W-TENG biosensors, while Yongchang Dong along with Apparao Rao and Ramakrishna Podila are developing new materials for replacing Teflon.